Ice
boxes are normally provided on boats, and for a day's cruise, serve
the purpose quite well, but for a longer cruise,
refrigeration provides a more varied menu and
plenty of cold drinks. In an ice box, food can
be kept no colder than 32 degrees F. and above
the ice level the temperature rises. Perishable
foods, such as meats and dairy products, will
deteriorate rapidly due to the growth of
bacteria and other organisms. By keeping these
products at a temperature from 30 to 50 degrees
F. they will last much longer. Refrigeration
will not kill the bacteria, but it does make
them dormant and prolongs the life of
perishables.

The most important
principle to remember is that refrigeration is a
process of removing heat from a matter by taking
the heat from one place and transferring it to
another. By using refrigerants (liquid gas)
piped through the various stages of the system,
the heat in one area can be absorbed and carried
to another area and released. This is
accomplished by the compression, condensation,
expansion, and evaporation stages of the
refrigerant as it is pumped through the system.

A good
boat refrigeration unit should keep frozen foods
frozen and other products cold but unfrozen for
days or weeks from an available energy source.
There are normally two sources of energy on a
boat and those are the ship's electrical power
or power from the engine. You must match your
refrigeration needs and desires with the energy
available as well as the box's size and shape.
In order to select the correct system for your
boat and your needs, you must give careful
consideration to the following factors.

REFRIGERATION BOX:
The size of the box and amount of insulation
must be evaluated by determining the following;
the type of insulation, the interior size or
cubic footage and the size and location of the
lid opening. Boxes of less than three cubic feet
are usually good candidates for 12-volt
refrigeration, but boxes larger than six cubic
feet are normally good candidates for engine
drive systems .

Before making a
decision, check the insulation. A good
refrigerator box normally has three or more
inches of polyurethane foam insulation and a
good freezer starts out with at least four or
more inches of polyurethane foam insulation.

The inside shape of
the box also determines how well the
refrigeration process will function. A tall
rectangular box with a top lid opening usually
provides the most even layering of cold. If the
evaporator or holding plate can be mounted high
in the box natural air tumbling will occur. This
will provide adequate cooling at all layers,
although, there will still be stratified layers
of cold. The bottom of the box will be the
coldest and the top of the box the warmest.

When dealing with long
flat boxes, the cold radiating from the holding
plate or the evaporator tends to cover the area
on an angle away from the evaporator or holding
plate. This means that the temperature will be
much colder up close to the refrigeration source
than the far end of the box. The temperature at
the far end, high in the box, will be warmer. So
some means must be adapted in the design to move
the cold into that area. I will feature box
design at a later date. So stay tuned!

The size of the lid
opening is very important in selecting your
equipment, since the evaporator or holding plate
that you choose must fit through the lid opening
and into the desirable position in the box. I
always recommend that before purchasing any
system that you construct a cardboard facsimile
of the holding plate or evaporator and place it
in the box to find out if it will fit through
the lid opening, or if it obstructs the access
to the box and the food product.

Before putting
together a refrigeration design for a particular
boat, I like to know what degree of
refrigeration we are talking about.
Refrigeration by melting ice provides a
temperature from 40-50 degrees F. and any
material embedded in the ice will beat 32
degrees F.. If a bag of ice is to be placed in a
box with refrigeration the ice will not melt if
the temperature in the box, where the ice is
stored, is maintained at 32 degrees F. or less.
If there is a desire to make ice, the
temperature in the box where the ice is to be
formed must be maintained at less than 32
degrees F. For example: at 25 degrees F. with
one tray it would take 12 to 24 hours for ice to
form a solid cube. If increased production is
required, it is desirable to have the
temperature from +6 to +8 degrees F.. This is
the temperature that the new home refrigerator
with an automatic ice maker is maintained, and
will produce six to eight trays a day. The
desire to have solid frozen ice cream on long
cruises will decide the degree of refrigeration
that will be required. Ice cream will stay in
the jelled form below 32 degrees F., but it will
not become frozen solid until it reaches 10
degrees F.. Usually the difference in
maintaining soft ice cream and hard ice cream is
to double the daily energy BTU requirement. This
is difficult for many people to understand. In
technical terms, when the Delta T is increased,
which is increasing the number of degrees of
temperature from ambient down to the lower box
temperature, the energy requirement is
drastically increased.

THE DAY
and WEEKEND SAILOR: The day sailor must decide
whether to refrigerate or buy ice. If a boat is
left anchored at a mooring unattended during the
week, refrigeration would be turned off, and
when the owner arrived for his sailing outing,
regardless of which system he had, it would have
to be run for a considerable length of time to
bring the box temperature down. Usually the
owner would bring ice to super cool the box. For
the day and weekend sailor who keeps his boat at
a dock where shore power is available, an
electrical system would be best as it would be
ready to go when he arrived, and products could
be left in the box from week to week.

FOR THE LIVE ABOARD WHO ANCHORS OUT:
There are a couple of options open to the
live-aboard. If his box is small enough and well
insulated, he could install a 12-volt system. If
the daily AMP hour requirements are greater than
50 and less than 140, he could consider
enhancing the system with a wind generator. If
the boxes are large and the refrigeration
requirements high, he would probably go with the
engine drive system. This would dictate the need
for running the engine on a daily basis. Twelve
volt units and wind generators can be used as
supplements, but it would be determined by the
daily BTU requirement.

FOR
THE LIVE ABOARD at the DOCK:For
the live-aboard who only goes sailing one day at
a time, a 110-volt system connected to holding
plates installed in the ice box will provide
more than adequate refrigeration. It is usually
best to install small ll0-volt systems of a
one-third horsepower or less. This avoids the
start up noise in the middle of the night as the
smaller units are quieter. If the boat is to be
used for cruising periodically, then an engine
drive system would be required, or if the box is
small with good insulation then a 12-volt unit
could be run off the batteries while at sea and
off the battery charger at the dock. Again this
would depend on the daily BTU requirements.

FOR THE LIVE ABOARD at FOREIGN DOCKS:
Because of the problem of obtaining 60 cycles,
115 volts in foreign ports, I strongly recommend
that the world cruiser consider 12-volt or
engine drive for foreign travel. The difference
between 50 and 60 cycles to the battery charger
is usually not a problem, although I would
suggest that a check with the manufacturer be
made first just to make sure.

REFRIGERATION for SPECIAL NEEDS:
Many beat owners want to put in refrigeration,
but some have a special refrigeration
requirement. There is the fisherman who wants to
freeze his catch, or just to pump cold water
through the fish box, and there is the cruiser
who requires a lot of cold beverages every day.
Other than finding a place to store these
products that is insulated and can be
refrigerated, the daily Btu requirement must be
determined. Again as a daily rule of thumb,
using the formula 600 Btu for each cubic foot of
refrigerator and 1000 Btu for each cubic foot of
freezer will give a fairly good "ball park"
figure for sizing the system.